Process for producing chlorosulfonated polyethylene using a mixed solvent

This application is a continuation of application Ser. No. 363,886, filed Mar. 31, 1982, now abandoned.

1. Field of the Invention

This invention relates to a process for performing the chlorosulfonation of polyethylene by chlorine and sulfuryl chloride or by sulfuryl chloride alone using a specific solvent.

2. Description of the Prior Art

It is known that an elastomer having excellent properties such as weather resistance, heat resistance, etc., is obtained by vulcanizing chlorosulfonated polyethylene having a chlorine content of 25-45% and a sulfur content of 0.3-4%.

The most important point in the case of producing chlorosulfonated polyethylene by dissolving polyethylene in a solvent and reacting the polyethylene with chlorine and sulfuryl chloride or sulfuryl chloride alone is how to uniformly distribute chlorine and a chlorosulfon group on polyethylene and the properties of chlorosulfonated polyethylene greatly change by the distributions of them.

Also, the chlorosulfonation of polyethylene is in the point of destroying the crystal of polyethylene and changing it into an amorphous substance and in this case, a sufficiently high temperature is necessary for fusing the crystals of polyethylene and it is said to be necessary to dissolve polyethylene at a temperature as high as possible and chlorosulfonate polyethylene at a high temperature.

However, in the case of using a low boiling point solvent such as carbon tetrachloride (boiling point 76.7° C.), which is generally used, it is very difficult to perform the uniform distribution of chlorine (U.S. Pat. No. 4,145,491) and even when a chlorination is performed to a considerable extent, the crystals of polyethylene remain in chlorosulfonated polyethylene formed.

Therefore, there is proposed a process of restraining the influence of the crystals of polyethylene as low as possible by performing the production of chlorosulfonated polyethylene in two steps, that is, by performing chlorination of polyethylene with chlorine at a temperature as high as possible (˜160° C.) in the first step to chlorinate to some extent and chlorosulfonating the polyethylene with sulfuryl chloride in the second step (see, U.S. Pat. No. 2,972,604). However, even in such a process, it is very difficult to establish the condition for obtaining a constant quality in the reaction using a low boiling temperature, such as carbon tetrachloride.

For overcoming the difficulty, a process may be considered wherein using a solvent having a high boiling point and a high dissolving power for polyethylene or the partially chlorinated product of it, polyethylene or the partially chlorinated product thereof is reacted in the solvent at a high temperature, but when such a high-boiling solvent is used, it is difficult to separate and recover the solvent from the polymer solution formed with a good efficiency as well as there are problems on the properties of the product. For example, when a drum drying method is employed for isolating chlorosulfonated polyethylene from the reaction mixture, the polymer formed must be isolated at temperature higher than the boiling point of the solvent used for the reaction and in this case, chlorosulfonated polyethylene is liable to color or deteriorate and also the solvent remains in the polymer to give various undesirable influences on the properties of the elastomer.

Accordingly, there is still a need for a process of producing a high quality chlorosulfonated polyethylene having an excellent quality of an elastomer while obtaining a constant quality product where the chlorine and chlorosulfone groups are uniformly distributed.

It is an object of this invention to provide a method to overcome the difficulties found in the reaction of producing chlorosulfonated polyethylene and the quality of the product. It is another object of the present invention to provide a process of producing chlorosulfonated polyethylene having excellent properties as elastomer by preventing the occurrence of reduction in properties of the product caused by the remaining crystals of polyethylene and the nonuniform distribution of chlorine, which is the undesirable problem in the foregoing conventional solution process using a low-boiling solvent and the reaction for producing chlorosulfonated polyethylene.

It is yet another object of the present invention to provide a process of producing chlorosulfonated polyethylene by dissolving polyethylene in a solvent and reacting the polyethylene with chlorine, and sulfuryl chloride or with sulfuryl chloride alone, wherein the reaction is performed using a mixed solvent composed of carbon tetrachloride and a halogenated aromatic compound, the content of the latter, i.e., the halogenated aromatic compound being in a range of 0.5-20% by weight of the total amount of the mixed solvent.

As the halogenated aromatic compound used in this invention, there are various kinds of mono- or tri-halogen substitution compounds containing a benzene ring but from an industrial viewpoint, chlorobenzene, chlorotoluene, iodobenzene, benzene fluoride, bromobenzene, etc. are particularly preferred in one embodiment of the present invention. The halogenated aromatic compound is contained in the mixed solvent in an amount of 0.5-20% by weight of the total amount of the mixed solvent but the preferable content thereof is 1-10% by weight. If the content of the halogenated aromatic compound is less than the aforesaid range, the chlorosulfonated polyethylene obtained does not exhibit the effects of this invention and shows inferior heat aging property and inferior low-temperature property although the tensile strength is excellent. On the other hand, if the content of the halogenated aromatic compound is higher than the aforesaid range, the chlorosulfonated polyethylene obtained is undesirably colored and emits a foul odor as well as the properties of the product, such as tensile strength, etc., become greatly inferior.

The chlorosulfonated polyethylene obtained by the process of this invention using the mixed solvent according to the teachings of this invention is excellent in character as elastomer as compared to those obtained using carbon tetrachloride alone as the reaction solvent and also excellent in properties such as workability and tensile strength as compared to the case of using a halogenated aromatic compound alone. That is, the chlorosulfonated polyethylene obtained by using carbon tetrachloride alone as the reaction solvent possesses high modulus and tensile characteristics caused by the insufficiency in solubility of polyethylene crystals in the low-boiling solvent and ununiformity of the distribution of chlorine as well as is inferior in low-temperature characteristics and workability and has higher plasticity. On the other hand, in the case of using a high-boiling halogenated aromatic compound such as, for example, chlorobenzene having a boiling point of 131° C., the solubility of polyethylene and the partially chlorinated product thereof is sufficiently high and the distribution of chlorine becomes uniform but the removal of the remaining solvent is difficult, which results in emitting a strong foul odor at compounding or fabricating the product, and the polymer obtained is, in particular, liable to color and is greatly inferior in tensile strength, compression set, etc., although the low-temperature characteristics thereof may be excellent. In yet another embodiment of the present invention, branched polyethylene obtained by a high-pressure polymerization process and straight chain polyethylene obtained by a medium-pressure or low-pressure polymerization process can be used as polyethylene to be chlorosulfonated and also ethylene copolymers containing up to 10% by weight monomer capable of copolymerizing with ethylene, such as, for example, propylene, butene-1, acrylic acid, vinyl acetate, etc., can be used in this invention and are included in the range of polyethylene in this invention.

Polyethylene is dissolved in the mixed solvent of carbon tetrachloride and a halogenated aromatic compound at a temperature of 90°-130° C. The proportion of polyethylene to the whole solvent is 2-20% by weight.

The chlorosulfonation of polyethylene is performed by reacting the polyethylene in the solution described above with chlorine and sulfuryl chloride or with sulfuryl chloride alone under pressure at a temperature of 60°-130° C. When polyethylene is reacted with sulfuryl chloride only, there is a feature that the reaction can be performed at a high temperature and a constant temperature from the beginning to the end of the reaction.

The chlorosulfonation reaction is usually performed using an azo compound such as azobisisobutyronitrile or a peroxide such as benzoyl peroxide as the reaction initiator and in the case of adding sulfuryl chloride, a tertiary amine such as pyridine is added as a catalyst.

Polyethylene is thus converted into chlorosulfonated polyethylene having a chlorine content of 25-45% and a sulfur content of 0.3-4% by such an operation. The reaction is performed in a glass-lined pressure vessel which is generally used for such a kind of reaction, the unreacted gas and produced gases formed during the reaction are released or removed from the system for maintaining the pressure in the vessel at a contstant pressure (0.5-5 kg/cm 2 ), and after the reaction is finished, the gases remaining in the system are removed by introducing an inert gas such as nitrogen into the system.

To the reaction solution of chlorosulfonated polyethylene thus obtained is, then, added a small amount of an epoxy compound such as a condensate of epichlorohydrin and bisphenol A as a stabilizer, and then the solution is supplied onto a drum heated so that the volatile contents in the chlorosulfonated polyethylene become below 1% and the chlorosulfonated polyethylene is continuously collected as a thin film while rotating slowly the drum.

Having generally described the invention, a more complete understanding an be obtained by reference to certain specific examples, which are provided therein for purposes of illustration only, and are not intended to be limiting unless otherwise specified. In addition, all parts and % in the examples are by weight unless otherwise indicated.